1. Field of the Invention
The present invention relates generally to a wafer surface machining apparatus, and more particularly to a wafer surface machining apparatus for grinding the reverse surface of a semiconductor wafer in a semiconductor wafer manufacturing process.
2. Description of Related Art
A surface machining apparatus for grinding the reverse surface of a semiconductor wafer generally comprises a housing stage for containing the wafers, a grinding stage for grinding the wafers, and a suction transfer device for transferring the wafers between the housing stage and the grinding stage. The conventional suction transfer device has a plurality of suction pads on a holding surface of a suction disc, and holds the wafers on the suction pads by suction.
Recently, there has been a desire for thin semiconductor wafers as ICs have become increasingly integrated. For this reason, the surface machining apparatus grinds the wafer thin.
The surface machining apparatus is provided with a chuck table, a grindstone, and a reverse surface cleaning device. The obverse surface of the semiconductor wafer is held on the chuck table and the grindstone is pressed against the reverse surface of the semiconductor wafer. The chuck table and the grindstone are rotated to grind the reverse surface of the wafer. On completion of the grinding, the wafer is removed from the chuck table, and then the reverse surface cleaning device cleans the reverse surface of the wafer.
An example of the reverse surface cleaning device is a spin cleaner. A chuck table of the spin cleaner holds the obverse surface of the wafer, and the chuck table is rotated while cleaning water is supplied to the reverse surface of the wafer to eliminate the sludge, etc. adhered to the reverse surface of the wafer.
Since microchips have been formed on the obverse surface of the wafer in a pretreatment, a protection film is attached on the obverse surface of the wafer in order to protect the microchips. The surface grinding apparatus grinds and cleans the wafer with the protection film attached thereon, and thereafter, the wafer is transferred to a protection film separation stage. For example, an adhesive tape is stuck on the protection film, and the protection film as well as the tape is peeled from the wafer.
Grinding the wafer thin decreases the strength of the wafer. In the case of the conventional suction disc that holds the wafer thereon with a plurality of suction pads, the peripheral part of the wafer easily chips or breaks during the transfer. Likewise, the wafer is damaged while the protection film is peeled from the wafer at the protection film separation stage.
In view of the foregoing, it is an object of the present invention to provide a wafer surface machining apparatus that has a suction transfer device capable of transferring the thin wafers without damaging them, and that prevents the wafers from being damaged at the protection film separation stage.
To achieve the above-mentioned object, the present invention is directed to a wafer surface machining apparatus comprising: a storage part for storing a wafer; a machining part for machining the wafer; and a suction transfer device for transferring the wafer between the storage part and the machining part, the suction transfer device holding the wafer on a suction disc having a holding surface composed of a porous member of substantially the same diameter as the wafer.
According to the present invention, the suction disc of the suction transfer device, which transfers the wafer between the storage part and the machining part, has the holding surface made of the porous member having substantially the same diameter as the wafer to thereby hold the entire surface of the wafer thereon. This prevents the thin wafer from chipping and breaking during the transfer.
To achieve the above-mentioned object, the present invention is directed to a wafer surface machining apparatus comprising: a table for holding a wafer; a machining member for machining the wafer; a driving part for moving the machining member and the table in such a direction as to become closer to one another to press the machining member against the wafer and rotating the machining member and the wafer relatively to one another to machine a first surface of the wafer; a first cleaning device for cleaning the first surface of the wafer after machining of the first surface; and a second cleaning device for cleaning a second surface of the wafer after the machining of the first surface, the second surface being opposed to the first surface.
It is understood that the sludge adhered to the protection film causes damage to the wafer during the protection film separation process. More specifically, if the sludge is adhered to the protection film, the adhesive tape cannot be stuck on the sludge adhering area completely. When the incomplete stuck tape is peeled from the wafer, the peeling force cannot uniformly be transmitted to the protection film. In this case, the peeling force may center on a part of the protection film, and the centered force damages the wafer. In particular, the sludge adhered to the outer peripheral part of the protection film causes damage.
To address this problem, the second cleaning device is provided to clean the protection film on the second surface or the obverse surface of the wafer to thereby eliminate the sludge from the protection film.
According to the present invention, the brush is employed in the second cleaning device. It is therefore possible to scrape the sludge from the protection film.
According to the present invention, the wafer after the surface machining is held on the suction disc of substantially the same diameter as the wafer. The transfer device transfers the wafer held on the suction disc to the second cleaning device. Since the entire surface is held on the suction disc, it is possible to transfer the wafer without damaging it and to uniformly clean the entire surface of the wafer, which is uniformly pressed against the second cleaning device. On the other hand, if the wafer is partially held on the conventional suction pads, the weight of the wafer is centered on the wafer holding sections on the suction pads. Therefore, the extremely thin wafer may be damaged during the transfer. Moreover, if the wafer is pressed against the cleaning means while the wafer is partially held on the conventional suction pads, there is a strong possibility that the wafer will be damaged during the cleaning. For this reason, it is much more effective to hold the wafer on the suction disc, which has substantially the same diameter as the wafer, in order to prevent the wafer from being damaged.
According to the present invention, the suction transfer device is supported by a supporting part on a body of the wafer surface machining apparatus, the supporting part having rigidity to withstand a reaction force generated when the second surface of the wafer is pressed against the second cleaning device. Thus, the entire second surface of the wafer is uniformly pressed against the brush, so that the entire second surface of the wafer can be cleaned uniformly. On the other hand, if the supporting part for the transfer means is conventionally provided with a cushioning means that cushions the pressing force against the wafer, the wafer cannot sufficiently be pressed against the brush and thus the wafer cannot be cleaned uniformly. For this reason, the rigidity of the supporting part is significantly effective for cleaning the surface of the wafer uniformly.
According to the present invention, the brush is a roller longer than the diameter of the wafer, and the brush is rotated about an axis of the roller and an axis perpendicular to the axis of the roller. It is therefore possible to clean the entire second surface of the wafer without rotating the wafer.